1. Field of the Invention
This invention relates to current pulse modulator circuits for use in radar applications and in particular to such modulators employing a pulse forming network to drive an rf generator.
2. Description of the Prior Art
The operation of current pulse modulators and their role in radar applications is well understood. The interested reader may find suitable background information in a number of U.S. Patents including:
______________________________________ U.S. Pat. No. Issue Date Inventor ______________________________________ 3,611,210 October 5, 1971 Theodore 3,737,679 June 5, 1973 Cooper 3,832,568 August 27, 1974 Wang 3,881,120 April 29, 1975 Osterwalder 4,001,598 January 4, 1977 Johannessen 4,099,128 July 4, 1978 Hooper 4,328,470 May 4, 1982 Bumgardner ______________________________________
Most of the pulse modulator circuits shown in the listed patents follow the traditional design of such circuits. The traditional design includes such elements as a pulse forming network (PFN) which is charged from a D.C. power supply through a charging choke and a holdoff diode. A trigger means (or switch) is coupled to the PFN and when triggered, causes the PFN to discharge through a load for generating microwave energy. The load device may be a tube device, a thyratron, or similar device which generally will not conduct in the reverse direction. Typically, the PFN is a multistage ladder network of inductors and capacitors. The trigger means is typically a silicon controlled rectifier (SCR) connected to the high side of the PFN. A pulse modulator design employing an IMPATT diode, but which does not use a ladder network of inductors and capacitors, is illustrated in the patent to Bumgardner. That patent also provides some helpful discussion of the nature and operation of the IMPATT diode. Such PFN of the prior art may have the capability of providing a pulse of adjustable duration or having adjustable feedback to tailor the source impedance and characteristics of the modulator to the particular IMPATT diode used, thereby improving operating efficiency, stability, and transient response. (See particularly Bumgardner, Col. 5, ll. 14-31.)